Extend am profile command to also collect lowoverhead traces.

Low overhead tracing is an experimental feature that is only enabled
when com.android.art.flags.Flags.alwaysEnableProfileCode is set. If this
isn't set we just log an error and ignore the request for tracing.

Usage:
adb shell am profile lowoverhead start <pid>
adb shell am profile lowoverhead stop <pid> [<path/to/file>]

File is optional when stopping the trace. If no file is provided then
trace data is simply discarded.

Test: manual test by capturing a trace
Bug: 352518093
Change-Id: Ie1ab526e0827b099a0d2f14ee170a2e0aca39d34